1. Technical Field
The present disclosure relates to a display device and a driving method thereof. The present disclosure also relates to an electronic apparatus that includes the display device. The present disclosure also relates to a signal processing method in the display device.
2. Description of the Related Art
In recent years, there has been an increasing demand for a display device for mobile apparatuses such as portable phones and electronic papers. In the display device, one pixel includes plural sub-pixels. The sub-pixels respectively output light of colors that differ from each other. One pixel can display various colors by switching ON/OFF the display of each of the sub-pixels. In some of the display devices, four sub-pixels including a white-color sub-pixel constitute one pixel (see Japanese Patent Application Laid-open Publications No. 2010-33009 (JP-A-2010-33009) and No. 2011-248352 (JP-A-2011-248352).
JP-A-2010-33009 describes a display device that includes an image display panel constituted by arraying pixels in a two-dimensional matrix, each of which is configured by first, second, third, and fourth sub-pixels, and a signal processing unit that accepts an input signal and outputs an output signal. The display device can add a fourth color to three primary colors to enlarge an HSV color space as compared to the case of the three primary colors. The signal processing unit has a maximum value Vmax(S) of brightness, where saturation S is a variable, stored therein, and obtains the saturation S and brightness V(S) based on a signal value of the input signal, and obtains an extension coefficient α based on at least one of values of Vmax(S)/V(S). The signal processing unit obtains an output signal value to the fourth sub-pixel based on at least respective input signal values to the first, second, and third sub-pixels, and calculates respective output signal values to the first, second, and third sub-pixels based on the input signal values, the extension coefficient α, and the fourth output signal value.
JP-A-2011-248352 describes a display device that includes a display panel in which plural pixels are provided, each of which includes sub-pixels that respectively include red, green, and blue color filters, and a sub-pixel that controls the light transmission of a white light, a backlight unit that includes red, green, blue and white light sources, an image switching circuit that switches the display mode of the display panel between a moving-image mode and a still-image mode, and a display control circuit that controls the luminance of red, green, and blue in the backlight unit according to an image signal in the moving-image mode, and that controls the luminance of the white light source in the backlight unit according to an image signal in the still-image mode.
As described in JP-A-2010-33009 and JP-A-2011-248352, an image signal is extended corresponding to an HSV region that is expanded by one sub-pixel (basically a white sub-pixel) of plural sub-pixels based on the image signal, to reduce the light amount of the light source and reproduce a desired image. An image can be brighter without increasing the light amount of the light source.
However, there is a case where an image viewer can recognize a change in the image when the light amount of the light source is changed. Therefore, it is preferable to control the light amount of the light source appropriately.
Japanese Patent Application Laid-open Publication No. 2010-169768 (JP-A-2010-169768) describes a video display device that calculates saturation based on signal values of video input signals of plural colors, that sets a value as a time constant that becomes larger as the saturation is higher, and that controls the light amount to be emitted from a white light source based on a target light amount and the time constant. However, the control of the light amount described in JP-A-2010-169768 is not appropriate in a case where the HSV region is expanded as described in JP-A-2010-33009 and JP-A-2011-248352.
For the foregoing reasons, there is a need for a display device, an electronic apparatus, a driving method of the display device, and a signal processing method capable of preventing an image viewer from recognizing a change in an image when an HSV color space is expanded.